1. Field of the Invention
This invention relates to a phase isolated type gas insulated switchgear containing components of each of three phases in separate vessels.
2. Description of the Related Art
Generally, gas insulated switchgears comprise devices containing a charging unit in a hermitically sealed metal vessel along with a highly insulating and arc-extinction insulation medium such as SF6 gas. If compared with air insulated switchgears, gas insulated switchgears can be remarkably downsized and hence can reduce the area of the installation site to a large extent by three-dimensionally arranging the circuit breakers, disconnectors and other required devices in order to reduce the gaps separating the devices. Additionally, since a gas insulated switchgear has a hermetically sealed structure, it provides an advantage of being scarcely influenced by external factors. For those reasons, gas insulated switchgears are being employed in substations and switching stations in and near large cities and also in costal regions from the viewpoint of poor availability of land and prevention of damages due to briny air.
Gas insulated switchgears of the categories of 72 kV to 300 kV containing the components of the three phases in a common vessel are being employed. However, in the voltage category of 240 kV and above, switchgears where the components of each of the three phases are separated from the components of the other phases are being popularly used in order to prevent problems of short-circuiting from taking place among the phases if a fault has occurred, because of the significance of such switchgears.
Such a phase isolated type gas insulated switchgear is typically connected to an operating mechanism comprising a power source and a control circuit of the power source for driving the internal electrodes of the circuit breakers. Similarly, the disconnector and maintenance earthning switch for the bus bar, the disconnector for the bus bar and the disconnector and maintenance earthning switch for the feeder line are connected to an operating mechanism for the disconnector and maintenance earthning switch, or an operating mechanism for the disconnector, whereas the fast earthning switch for the feeder line is connected to an operating mechanism for the fast earthning switch.
The inside of a gas insulated switchgear is filled with a gaseous insulating medium. The switchgear is equipped with a gas gauge for monitoring the pressure or the density of the internal gaseous insulating medium, because the insulation performance of the switchgear relies on the pressure or the density of the gaseous insulating medium. When a fast earthning switch is contained in a same gas division with a disconnector and maintenance earthning switch for a feeder line, a common gas gauge is used for monitoring the pressure or the density.
The operating mechanism needs to be driven or serviced by an operator and the reading of the gas gauge needs to be visually checked by the operator when driving or servicing, whichever appropriate, the gas insulated switchgear so that the gas gauge should be accessible to men.
As gas insulated switchgears are downsized in pursuit of economy, it becomes difficult to secure a space for monitoring and servicing operations where the operator can access and service the gas insulated switchgear. The net result is a degraded serviceability/operability. Differently speaking, the efforts for downsizing gas insulated switchgears confront limitations because a space needs to be secured for servicing operations. Thus, the need of such a space makes it difficult to realize an economic gas insulated switchgear.
A local control panel of a conventional gas insulated switchgear is normally separated from the switchgear itself. The local control panel contains the operation handles, or the switches, of the circuit breaker, the disconnector and the earthning switch of the feeder line and the circuits that electrically realize the interlocking requirements of the feeder line. The local control panel also contains a circuit for receiving and displaying electric signals from the detector for electrically detecting a defective condition of the gas insulated switchgear that may be a gas pressure decrease or a gas density decrease. The local control panel additionally contains an electric/electronic circuit for electrically transmitting information to the host system, a circuit for transmitting signals for driving the switches of the feeder line in response to a switch operation command from the host system, a power supply distributing circuit to be used to control/operate the feeder line.
Then, the operating mechanisms of all the circuit breakers, the disconnector and maintenance earthning switches and other devices and the gas gauge of the feeder line are electrically connected to the local control panel for controlling/monitoring the feeder line by way of a low voltage control cable. Ducts, trays, wire tubes and other incidental equipment for supporting and/or protecting the low voltage control cable are arranged between the gas insulated switchgear main body and the local control panel. A space is secured to install and operate the local control panel itself.
Japanese Patent Application Laid-Open Publication No. 2-23008 (the entire content of which is incorporated herein by reference) discloses a gas insulated switchgear that is devised to save space and show improved operability/serviceability. In the gas insulated switchgear disclosed in the above-cited Japanese Patent document, the disconnector and maintenance earthning switches are contained in the circuit breaker vessel and the tube table for leading out the drive shaft is extended so as to arrange the operating mechanisms to the front surface of the switchgear in a concentrated manner. However, the disclosed switchgear is of the three-phase common type and cannot be applied straightly to a switchgear where the disconnectors and the circuit breakers of each phase are separated from those of the other phases by gas compartments. Additionally, it is not possible to arrange the operating mechanisms in parallel in a horizontal direction with disclosed technique. Therefore, if the operating mechanisms of a phase isolated type gas insulated switchgear are arranged in a concentrated manner, the height of the operating mechanism side of the switchgear cannot be reduced and hence the efficiency of operation of the switchgear is not improved satisfactorily because the phase isolated type gas insulated switchgear has a height significantly greater than the three-phase common type switchgear (See FIG. 1 of the above-cited Japanese Patent document).